SHARPSBURG, Md. — Members of the Ku Klux Klan and other white supremacist groups rallied Saturday at the Antietam National Battlefield, believed to be the first time a group was given permission to demonstrate at the site of the bloodiest day of the Civil War.

About 30 people, some in white robes and others in the military-style clothing and swastika armbands of the National Socialist Movement of America, stood next to a farmhouse on the battlefield. Some delivered speeches attacking immigrants, blacks and other minority groups.

About 200 federal, state and local officers watched to ensure peace and to act as a buffer between the Klan and about 30 counter-demonstrators.

Antietam carries powerful symbolism, said Gordon Young of the Ku Klux Klan.

“As the Klan, we are the ghosts of our Confederate brothers and sisters who died here,” Young said.

The protest was the third by extremist groups at national parks in the past three years. Two years ago, the National Socialist Movement demonstrated at Valley Forge, Pa., and the same group rallied last year at Colonial Park in Williamsburg, Va.

“The Supreme Court has ruled consistently that national parks in particular are places of freedom of expression,” said park superintendent John Howard.

Said Jeffrey Margolies, a counter-demonstrator from the Jewish motorcycle group Semites on Bikes: “It’s disgusting that they would come to sacred ground.”

Union and Confederate forces clashed Sept. 17, 1862, on farmland about 40 miles outside Washington during Confederate Gen. Robert E. Lee’s first invasion of the North. More than 3,600 men on both sides died that day, and more than 19,000 were wounded or went missing, according to the park service.